Private pilot · ACS PA.I.G
Operation of Systems
Know your airplane's systems well enough to explain how they work, recognize a failure, and handle it.
Your POH is the source for your specific airplane; this lesson covers the typical training airplane.
Why this one matters
System failures rarely cause accidents by themselves; the pilot's response does. Knowing how each system works lets you spot a failure early from the instruments, understand what it means, and handle it calmly with the checklist instead of being surprised.
Can’t miss
- •The magnetos make ignition independently of the airplane's electrical system; the engine keeps running if the alternator or battery fails.(PHAK (FAA-H-8083-25C), Aircraft Systems)
- •Carburetor ice can form in a wide range of temperatures with visible moisture or high humidity. Sign in a fixed-pitch airplane: dropping RPM. Fix: full carburetor heat.(PHAK (FAA-H-8083-25C), Aircraft Systems)
- •Pitot-static: the airspeed indicator uses pitot and static; the altimeter and VSI use static only.(PHAK (FAA-H-8083-25C), Flight Instruments)
- •Vacuum failure: the attitude and heading indicators slowly become unreliable. Cross-check, cover them, and fly by the other instruments.(PHAK (FAA-H-8083-25C), Flight Instruments)
- •Alternator failure: the battery is all you have. Reduce electrical load and land as soon as practical.(PHAK (FAA-H-8083-25C), Aircraft Systems)
- •Above 12,500 feet MSL for more than 30 minutes, and at all times above 14,000, the crew must use oxygen.(14 CFR 91.211)
- •For any abnormality: fly the airplane, then the checklist, then decide and communicate.(PHAK (FAA-H-8083-25C), Aircraft Systems)
What you should know
Flight controls K1
- Primary controls: ailerons (roll), elevator (pitch), rudder (yaw).(PHAK (FAA-H-8083-25C), Flight Controls)
- Secondary controls: flaps (more lift and drag, lower stall speed), trim (relieves control pressure) and, on some airplanes, spoilers.(PHAK (FAA-H-8083-25C), Flight Controls)
Engine, propeller, fuel and oil K1
- Most training airplanes have a four-stroke (intake, compression, power, exhaust), horizontally opposed, air-cooled piston engine.(PHAK (FAA-H-8083-25C), Aircraft Systems)
- Dual magnetos give two independent ignition systems; the run-up checks each one.(PHAK (FAA-H-8083-25C), Aircraft Systems)
- Lean only as the POH directs: normally in cruise at 75% power or less, or at high density altitude. Don't lean aggressively for takeoff or a full-power climb, enrich before adding power or descending, and watch cylinder and oil temperatures.(PHAK (FAA-H-8083-25C), Aircraft Systems)
- Carburetor ice forms from fuel vaporization and the venturi effect, even well above freezing with humid air. It is most likely below about 70°F (21°C) with relative humidity above 80%, and can form at much warmer temperatures because the carburetor air can be up to about 70°F colder than outside. The risk is highest at low power: apply full carb heat before reducing power for a descent. Expect a further drop as the ice melts, and leave it on until RPM (fixed pitch) or manifold pressure (constant speed) recovers.(PHAK (FAA-H-8083-25C), Aircraft Systems)
- Fuel-injected engines can't get carburetor ice, but they can get induction (impact) icing that blocks the air intake or filter. Use the alternate air source per the POH.(PHAK (FAA-H-8083-25C), Aircraft Systems)
- Fixed-pitch propellers are set for one compromise. With a constant-speed propeller, the throttle sets manifold pressure (power, on the MP gauge) and the propeller control sets RPM, which the governor holds. Reducing power: manifold pressure first, then RPM. Increasing power: RPM first, then manifold pressure. Avoid high MP with low RPM beyond the POH limits.(PHAK (FAA-H-8083-25C), Aircraft Systems)
- High-wing airplanes often feed fuel by gravity; low-wing airplanes need fuel pumps. Sump the tanks before flight to check for water and contamination; 100LL avgas is blue.(PHAK (FAA-H-8083-25C), Aircraft Systems)
- Detonation is explosive, uncontrolled burning of the mixture after normal spark ignition, from excess heat and pressure, low-grade fuel or overheating: reduce power, enrich the mixture and increase cooling. Preignition is ignition before the spark, from a hot spot such as a glowing deposit or damaged plug; it can cause detonation, roughness and severe damage.(PHAK (FAA-H-8083-25C), Aircraft Systems)
- Oil lubricates, cools, seals and cleans. Read the pressure and temperature together: low pressure with rising or high temperature means oil loss and coming engine failure, so land as soon as possible; low pressure with normal temperature is more likely a gauge or sensor fault, so monitor, follow the POH and land as soon as practical.(PHAK (FAA-H-8083-25C), Aircraft Systems)
Electrical, landing gear and the cabin K1
- The alternator (or generator) powers the system and charges the battery; the master switch connects them. A center-zero ammeter shows the battery charging (+) or discharging (-): a discharge in flight means the alternator isn't carrying the load. A loadmeter shows the alternator's output: zero in flight means it has failed.(PHAK (FAA-H-8083-25C), Aircraft Systems)
- Hydraulics: pressurized fluid from a reservoir operates the wheel brakes in most trainers, and gear or flaps in some. Check brake feel and fluid per the POH; losing pressure means weak or no brakes (and gear or flap problems where fitted, with the emergency gear extension).(PHAK (FAA-H-8083-25C), Aircraft Systems)
- Landing gear may be fixed or retractable; know your gear and brake systems and their checks.(PHAK (FAA-H-8083-25C), Aircraft Systems)
- Cabin heat usually comes from a shroud around the exhaust. An exhaust leak can put carbon monoxide in the cabin: carry a CO detector.(PHAK (FAA-H-8083-25C), Aircraft Systems)
- Anti-ice prevents ice from forming (pitot heat, carburetor heat, heated windshields and propellers, fluid systems); deice removes it after it forms (pneumatic boots, weeping-wing fluid). A typical trainer has only pitot heat, carb heat and defrost and is not approved for known icing: avoid icing, and leave it at once if you meet it.(PHAK (FAA-H-8083-25C), Aircraft Systems)
- Supplemental oxygen: crew above 12,500 to 14,000 feet MSL for more than 30 minutes, crew at all times above 14,000, and every occupant must be provided oxygen above 15,000.(14 CFR 91.211)
Flight instruments K1
- Pitot-static instruments: airspeed indicator (pitot and static pressure), altimeter and vertical speed indicator (static only).(PHAK (FAA-H-8083-25C), Flight Instruments)
- Gyroscopic instruments: the attitude and heading indicators are usually vacuum-driven; the turn coordinator is usually electric, so one failure doesn't take all of them.(PHAK (FAA-H-8083-25C), Flight Instruments)
- Glass cockpits replace these with an AHRS and an air data computer, with backup instruments. Know your backups.(PHAK (FAA-H-8083-25C), Flight Instruments)
Recognizing and handling failures K2 · R1 · R2
- Blocked pitot tube, drain hole open: the airspeed drops to zero, while the altimeter and VSI work normally. Pitot inlet and drain both blocked (static open): the airspeed indicator acts like an altimeter, rising in a climb, falling in a descent and not responding to speed changes in level flight.(PHAK (FAA-H-8083-25C), Flight Instruments)
- Blocked static port: the altimeter freezes, the VSI reads zero, and the airspeed reads low when you are above the altitude where it blocked and high below it. Open the alternate static source: the altimeter and airspeed usually read slightly high, the VSI shows a momentary climb before settling, and the POH may give a correction table.(PHAK (FAA-H-8083-25C), Flight Instruments)
- Vacuum failure: the suction gauge drops and the attitude and heading indicators drift. Cross-check against the turn coordinator, airspeed and altimeter.(PHAK (FAA-H-8083-25C), Flight Instruments)
- Alternator failure: the ammeter shows a discharge or the low-voltage light comes on. Turn off non-essential electrical equipment and land as soon as practical.(PHAK (FAA-H-8083-25C), Aircraft Systems)
- Rough engine: work the POH checklist in order (carburetor heat, throttle, mixture, fuel pump where fitted, fuel selector to the tank with the most fuel, primer locked) and pick a landing site. For the magnetos, try left, then right, then back to both; never select off in flight. If it runs smoothly on one magneto, stay on that one and land.(PHAK (FAA-H-8083-25C), Aircraft Systems)
- Scan the engine and system gauges regularly; early detection gives you time.(PHAK (FAA-H-8083-25C), Aircraft Systems)
Automation R3
- Autopilots and GPS reduce workload but can fail or be set wrong. Know what mode it's in and what it will do next, and be ready to hand-fly.(PHAK (FAA-H-8083-25C), Flight Instruments; Advanced Avionics Handbook)
- If the automation surprises you, disconnect it and fly.(Risk Management Handbook (FAA-H-8083-2A))
Avionics in your airplane K1 · R3
- Know the installed avionics in the airplane you fly: communication and navigation radios, GPS, transponder and ADS-B, the audio panel and intercom, the autopilot, and on a glass panel the AHRS, air data computer and backup instruments. For each, know what it does, what powers it, and what you lose when it fails, from the POH and the avionics manuals.(PHAK (FAA-H-8083-25C), Flight Instruments; Advanced Avionics Handbook (FAA-H-8083-6))
Scenarios
Decide what you would do first, then see the worked answer.
Climbing through clouds you didn't expect, the airspeed indicator shows a steady increase while you're climbing at constant power.
What's wrong? See the worked answer
A blocked pitot tube with the drain hole blocked too: trapped pressure makes it act like an altimeter. Turn on pitot heat, use known pitch and power settings, and don't trust the airspeed indication.
PHAK (FAA-H-8083-25C), Flight Instruments
At night, the low-voltage light comes on and the ammeter shows a discharge.
What do you do? See the worked answer
Follow the POH checklist: check the alternator circuit breaker and switch. If it won't reset, reduce load (keep essential lights and one radio), tell ATC, and land at the nearest suitable airport before the battery runs down.
PHAK (FAA-H-8083-25C), Aircraft Systems
With the cabin heat on, you get a headache and feel drowsy.
What could it be, and what do you do? See the worked answer
Carbon monoxide from an exhaust leak. Turn off the cabin heat, open the fresh-air vents, use oxygen if you have it, and land as soon as possible.
PHAK (FAA-H-8083-25C), Aircraft Systems
Common mistakes
Saying the engine stops if the electrical system fails.
Magnetos are self-contained.
Instead: Know which systems depend on electrical power and which don't.
Removing carb heat when the RPM first drops further.
The drop means ice is melting through the engine.
Instead: Leave full carb heat on until the RPM recovers and stays steady.
Trusting a failed attitude indicator.
A vacuum failure fails slowly and silently.
Instead: Cross-check the instruments and check the suction gauge in your scan.
Now train it
Say it out loud, hear it asked, and take the quick check in this lesson’s practice pack. It tracks your shaky spots.
Got it?
When it feels solid, practice operation of systems out loud with our examiner.
Your progress is saved in this browser. Create a free account to keep it on every device, with your shaky spots and mock oral results in one place.
Go to the source (free)
Teaching this? The instructor lesson plan →
Sources
- Pilot's Handbook of Aeronautical Knowledge (FAA-H-8083-25C): Flight Controls; Aircraft Systems; Flight Instruments
- Advanced Avionics Handbook (FAA-H-8083-6)
- 14 CFR 91.211
- Your airplane's POH/AFM: systems description and emergency procedures
Study aid, not FAA guidance. Regulations change; check the current text at eCFR and the ACS. Checked against current sources 2026-11-12.